He joined two other MPs, Giorgos Germenis and Panayiotis Iliopoulos, who were also put behind bars at the weekend. All three face charges of joining and directing a criminal organization.

In response to his client being placed in custody, Boukouras's lawyer, Alexis Kougias, warned that «Greece is heading to a democratic breakdown».

All three lawmakers, who have had their parliamentary immunity lifted, deny the charges, claiming that Golden Dawn is not a criminal organization and that they are victims of a «political persecution».

Three other Golden Dawn MPs, among them the leader Nikos Michaloliakos, have been put in custody since late September.

A further three, including party spokesman Ilias Kasidiaris have been charged too in connection with the investigation but are not in custody.

Tensions were running high outside the magistrate's office on Sunday.

Journalists asked Kasidiaris to denounce Golden Dawn supporters throwing of bottles of water and shouting of threats against them, on Saturday night, after they heard the decision regarding the two first MPs.

Kasidiaris refused to do this, so journalists refrained from reporting his comments, according to the state-run Athens News Agency.

Golden Dawn has announced its intention to challenge the Greek government's crackdown in the European Court of Human Rights and branded the procedures leading to the pre-trial detention of Michaloliakos and other MPs as «illegal and unconstitutional».

The crackdown against the neo-Nazi party which, according to prosecutors, has revealed the group's violent paramilitary activities, was prompted by the killing of leftist rapper Pavlos Fyssas by a member of Golden Dawn, in September.

Golden Dawn, which entered Greeces 300-seat parliament for the first time after elections in June 2012, remains the third most popular party in polls and has seen a jump in its approval rating amid public frustration over the deep recession in Greece.